Gutenberg Open Science

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ZeitschriftenaufsatzAccess status: Open Access ,
Retention during freezing of raindrops – Part 2 : Investigation of ambient organics from Beijing urban aerosol samples
(2025) Seymore, Jackson; Gautam, Martanda; Szakáll, Miklós; Theis, Alexander; Hoffmann, Thorsten; Ma, Jialiang; Zhou, Lingli; Vogel, Alexander L.
The freezing of hydrometeors causes certain water-soluble organic compounds dissolved in the supercooled cloud droplets to be released into the gas phase. This may lead to the vertical redistribution of substances that become available for atmospheric processes in the upper troposphere, such as new particle formation or ozone formation. Drop-freezing experiments were performed on the Mainz acoustic levitator (M-AL) using aqueous extracts of ambient samples of Beijing urban aerosol. The retention coefficients of over 450 compounds were determined. Most nitro-aromatics and organosulfates were fully retained, along with the aliphatic amines (AAs) and higher-order amines and amides, while the observed sulfides, lipids, aromatic hydrocarbons, and long-chain compounds are among the most unretained and, incidentally, are the fewest species present. The findings here also indicate that N- and S-containing compounds, primarily nitro and sulfate components of secondary organic aerosols (SOAs) anthropogenically related to NOx and SO2 chemistry, have enhanced retention, likely due to their increased polarity. An insignificant positive correlation between polarity and freezing retention, along with a significant negative correlation with vapor pressure and freezing retention, was observed. No sigmoidal relationship with the effective Henry's law constant was observed. This differs from the parameterizations of riming retention presented in the current literature, which is justified by the lower surface-to-volume ratio of the large drop size investigated. This study greatly expands upon the available experimental measurements of retention by investigating hundreds of compounds in complex chemical conditions that are more similar to the atmosphere than in previous literature studies.
ZeitschriftenaufsatzAccess status: Open Access ,
Retention during freezing of raindrops – Part 1 : Investigation of single and binary mixtures of nitric, formic, and acetic acids and 2-nitrophenol
(2025) Gautam, Martanda; Theis, Alexander; Seymore, Jackson; Hey, Moritz; Borrmann, Stephan; Diehl, Karoline; Mitra, Subir K.; Szakáll, Miklós
The influence of freezing processes and vertical transport of trace gases into the upper atmosphere during deep convection is critical to understanding the distribution of aerosol precursors and their climate effects. We conducted experimental studies inside a walk-in cold room for freely levitating raindrops (drop diameter: 2 mm) using an acoustic levitator apparatus. We investigated the effect of freezing raindrops on the retention of organic species for the first time with silver iodide as the ice-nucleating agent. Quantitative chemical analysis determined the retention coefficient, which is defined as the fraction of a chemical species remaining in the ice phase compared to their initial liquid-phase concentrations. We measured the retention coefficients of nitric acid, formic acid, acetic acid, and 2-nitrophenol as single components. Furthermore, we determined the retention coefficients of these substances as binary mixtures. Our results show the dominance of physical aspects such as drop size and ice shell formation over their chemical counterparts with regard to overall retention for the investigated large drops. Thus, for rain-sized drops, almost everything is fully retained during the freezing process, i.e., retention coefficients close to 1, even for species with low effective Henry's law constants (H ∗ < 10−4). An ice shell is formed within 4.8 ms around the drops just after the freezing is initiated. This ice shell formation was found to be the controlling factor for the overall retention of the investigated species, which inhibited any further expulsion of dissolved substances from the drop.
ZeitschriftenaufsatzAccess status: Open Access ,
A dilatant visco-elasto-viscoplasticity model with globally continuous tensile cap : stable two-field mixed formulation
(2025) Popov, Anton A.; Berlie, Nicolas; Kaus, Boris J. P.
Rocks break if shear stresses exceed their strength. It is therefore important for typical geoscientific applications to take shear failure mechanism and the subsequent development of mode-II shear bands or faults into account. Many existing codes incorporate non-associated Drucker-Prager or Mohr-Coulomb plasticity models to simulate this behavior. Yet, when effective mean stress becomes extensional, for example when fluid pressure becomes large, the dominant failure mode changes to a mode-I (opening) mode, which initiates plastic volumetric deformation. It is rather difficult to represent both failure modes in numerical models in a self-consistent manner, while also accounting for the nonlinear visco-elastic host rock rheology, which varies from being nearly incompressible in the mantle to being compressible in surface-near regions. Here, we present a simple plasticity model that is designed to overcome these difficulties. We employ a combination of a linearized Drucker-Prager shear failure envelope with a circular tensile cap function in way that ensures continuity and smoothness of both yield surface and flow potential in the entire stress space. A Perzyna-type viscoplastic regularization ensures that the resulting localization zones are mesh-insensitive. To deal with the near incompressibility condition, a mixed two-field finite element formulation is employed. The local nonlinear iterations at the integration-point level are used to determine the stress increments. The global Newton-Raphson iterations are applied to solve the discretized momentum and continuity residual equations. The presented plasticity model is implemented in an open-source 2D unstructured finite element code GeoTech2D. The results of several typical test cases that range from crustal scale deformation to the propagation of fluid-induced tensile failure zones demonstrate rapid convergence. The robustness of the solution scheme is enhanced by the adaptive time stepping algorithm.